1. Field of the Invention
This invention relates to the joining of tubes or pipes, and more particularly, to an aseptic flanged joint between pipes employing a self-aligning rigid retaining ring surrounding a gasket and limiting the deformation thereof.
2. Description of the Prior Art
Flanged joints are widely used to interconnect tubes or pipes conveying a variety of fluids, including gases, liquids, liquids also containing solid or semi-solid matter, or other fluid-like media. The tubes may be either pressurized or under vacuum. The joints connect extended sections of tubes, as well as joining tubes to fittings, couplers, valves, pumps, inspection ports, and other related devices. An ideal joint is easily assembled with minimal cost and labor, and is capable of operating reliably under any conditions reasonably anticipated during its service life. It is essential that the joint remain sealed to prevent leakage either into or out of the system in which the tube is used. The materials comprised in the joint must be chemically and thermally compatible under operating conditions with substances they will contact and the surfaces of the joint fittings. In many cases, it is further required that the joint be easily disassembled for repair and maintenance operations, including the cleaning and sanitizing of systems and replacement of gaskets or the like. Ideally, the presence of the joint does not introduce any protrusion or other interruption of the uniform surface inside the piping that would increase the flow resistance of the piping, e.g. by disrupting or impeding the smooth flow of fluid therethrough.
The requirements for joints, including flanged joints, used in process systems that convey food, beverage, pharmaceutical, personal care, or other like products intended for human or animal use through ingestion or external application are especially demanding. These systems must be maintained under strictly aseptic conditions. As used herein and in the subjoined claims with reference to a process system, the term “aseptic condition” is understood to mean a condition in which there is substantially no growth of unwanted or pathogenic organisms and substantially no buildup of debris or other medium in which such organisms are likely to reproduce or be trapped, agglomerated, concentrated, or otherwise situated in a manner that is likely to contaminate any substance passing through the system. The term “aseptic product” is to be understood as referring to any of the aforementioned products that ordinarily must be processed under aseptic conditions. Moreover, no materials can be used in aseptic joint systems that would introduce any harmful or objectionable substances into the process stream for the aforementioned aseptic products. Many piping and joint systems that might be acceptable for general chemical or industrial processing are not able to satisfy one or more of the stringent requirements associated with processing aseptic products. For example, some known joint systems have a configuration wherein recesses, crevasses, O-ring grooves, or the like result in dead spaces or stagnation regions in which there is little or no flow of the fluid being transported. As a result, accumulation of debris likely to give rise to the accumulation and reproduction of pathogens is a serious concern. Also, some known gasket materials may impart objectionable flavors or even toxic substances into food, beverages, or pharmaceuticals. Furthermore, the use of certain substances that come into contact with the process fluid may be offensive to adherents of certain religious traditions.
A variety of techniques are in widespread use for making interconnections. Flanged joints employing deformable gasket material that is interposed between the flanges and deformed by axial compression between the flanges are commonly used. Various materials have been used for such gaskets, such as elastomeric materials, impregnated fibrous materials, and soft metal sheets. One form of such joint and seal is depicted generally at 9 in FIG. 1. Joint 9 connects generally cylindrical tubes 12, 14, which are attached to flanges 6, 8 (also known as ferrules) by welding 11, as shown, or by various other known techniques. Flanges 6 and 8 adjoin in end-to-end relationship about a common center axis 19. The flanges are substantially identical and have mating faces generally perpendicular to axis 19. Opposite the mating face of each flange is a clamping face including tapered section 36. When flanges 6 and 8 are mated, respective sections 36 cooperate to form a generally frustoconical peripheral surface. The joint is secured using clamp 40 and sealed using O-ring gasket 17. The flanges used on each side of joint 9 are substantially identical in shape.
The mating face surface of flanges 6 and 8 has an inner portion 30 and an outer portion 34 that are generally co-planar, along with an intermediate circumferential groove or recess 32 that accommodates gasket 17, which is in the form of a synthetic rubber O-ring, i.e. a cylindrical gasket having the shape of a torus or donut. The O-ring is located and received in grooves 32. Normally flanges 6 and 8 both include a groove 32. However, joints are sometimes used in which a groove is provided in only one of the flanges, the other flange having a fully planar mating surface. Of course, the groove in such embodiments must be correspondingly deeper. In other instances, the gasket is a cylindrical O-ring with a rectangular cross-section (not shown) instead of the more commonly used circular cross-section.
Joint 9 is secured with a split-ring clamp 40, which is ordinarily composed of metal. A major portion of the inner circumferential surface of clamp 40 has a V-shape with tapered surface portions 42. These tapered surfaces encircle and securingly engage correspondingly tapered outer sections 36 of flanges 6 and 8. Clamp 40 is split into a plurality of arc-like segments. As further illustrated in the form depicted in FIG. 2, clamp 40 has two generally semicircular arc segments 50, 52, each subtending an angle slightly less than 180°. Segments 50 and 52 are both bifurcated at each of their ends. A rigid linkage 54 joins ends 51 and 53 of segments 50 and 52, respectively, and is disposed between the furcations. Retaining pins 55 pass through and are secured in holes in ends 51 and 53. Pins 55 also pass freely through holes in opposite ends of linkage 54 to create rotatable joints between the segments 50, 52 and linkage 54, allowing segments 50 and 52 to pivot about pin 55 within a common plane. The opposite ends of segments 50 and 52 have enlarged, furcated ends 58 and 59, respectively. A retaining pin 62 passes through and is secured in holes in end 59. Pin 62 also passes freely through the eye of threaded eyebolt 60, which is located between the furcations of end 59. To secure the clamp, the free end of eyebolt 60 is rotated about pin 62 and into the space between the furcations of end 58. A threaded nut 64 is tightened onto eyebolt 60 and against a flat surface of furcated end 58 to place clamp 40 in closed position, as shown in FIG. 2.
The tightening of nut 64 acts to reduce the effective circumference of clamp 40. The resulting wedging of frustoconically tapered inner clamp surface 42 over opposed, complementary frustoconical sections 36 of the two flanges imparts an axially directed force urging the flanges together. Proper design of joint 9 requires that the degree of tightening clamp 40 that brings corresponding surfaces 30 and 34 of flanges 6 and 8 into contact causes a requisite degree of compression of O-ring 17. Proper sealing is effected if O-ring 17 substantially fills grooves 32 of both flanges, with contact between O-ring 17 and grooves 32 on each side that extends around the full circumference of each flange.
However, in practice a number of problems occur in reliably effecting seals using joints of the type depicted by FIG. 1. Ideally, both the application of clamp 40 depicted in FIG. 1 and the full seating of O-ring 17 in respective facing grooves 32 provide the required lateral alignment of the opposed flanges. At best, O-ring 17 provides only minimal lateral alignment of respective grooves 32. It is frequently found that joints are made up with the flanges not fully coaxially aligned. As a result, the corresponding grooves 32 in the two flanges are not aligned and O-ring 17 often is not fully and properly seated in both grooves 32. In this circumstance, tightening of clamp 40 may compress at least part of O-ring 17 between surfaces 30 or 34. Damage to the O-ring is likely, especially in parts that traverse the edges between groove 32 and the adjacent planar surfaces 30 or 34. Premature failure of the O-ring to seal commonly results. Moreover, surfaces 30 and 34 may not properly seat in this situation, in many cases creating a recess between surfaces 30 into which process fluid present in tubes 12 and 14 can collect. In some cases such a recess communicates with portions of groove 32 not filled with O-ring 17, increasing the likelihood of untoward consequences, such as microbial activity as described in detail above. A joint system that more positively assures proper alignment and a durable, effective seal is thus highly sought.
Moreover, even if the flanges are accurately aligned and the O-ring seal properly disposed in its grooves, the joint system of FIGS. 1-2 is prone to certain difficulties. The axial impingement of the mating flanges after the clamp is secured is limited by metal-to-metal contact of the flange faces. In some cases, especially after wear and tear that attends repeated assembly and disassembly of the flanged joint, contact occurs in regions 34, leaving some space between facing inner surface regions 30. Frequently, such an area becomes a trap, with the deleterious consequences set forth above.
In many applications, O-ring 17 must be replaced periodically. In some industrial manufacturing processes, required system repairs or periodic preventive maintenance dictate that flanged joints be disassembled and reassembled frequently. Exposure to required processing temperatures or to corrosive or abrasive process fluids in some cases causes seal materials to erode. Some materials are embrittled over time by exposure to their process environment. Moreover, many seal materials exhibit creep or related mechanical phenomena or otherwise lose their elasticity and take a permanent “set.” Joints that are clamped together repeatedly despite poor alignment also are likely to result in wear or damage (e.g. scratching) to mating surfaces 30, 34, which may also compromise seal integrity. Cleaning and sanitary protocols demand regular service of joints and replacement of seals in still other instances. The actual cost of the O-ring and other elastomeric components typically is small in comparison with the labor costs for their replacement and the losses due to manufacturing downtime. However, the metal parts of the joint are generally far more expensive due to the precision machining and dimensional control needed. As a result, it is highly desired that metal parts be reusable.
Notwithstanding numerous improvements in the materials and configurations known for flanged joints, there remains a need in the art for a joint system that is inexpensive to construct and simple to maintain, yet provide reliable and robust service. It is further desirable that the system can be serviced by workers who do not need extensive training or a high skill level yet can accomplish needed repairs expeditiously to minimize costly downtime in a process system.